LINEAR TRANSVEKTER By Dave Mascaro, WASJUF, RD 1 Box 467, Ottsville, Pennsylvania 18942

verthe past few years Amateur microwave activity in the United States has increased

dramatically. Many operators active on 1296 MHz have put their stations on the 2304-MHz band. Stationswork 10-GHz SSBICW, as well as wide-band FM with Gunnplexers?There's more com- mercial equipment available for all bands up to 10 GHz. Homebrewers are using surplus l V receive only (NROI

I didn't use a 144-MHz i-f post ampli- fier after the receive mixer. Unlike the 28-MHz "front end" in an HF trans- ceiver that is normally used for a trans- verter, modern 2-meter transceivers have good front ends with plenty of gain. A post amplifier only makes the resting S-meter readings higher. The system noise figure is established in the 34%-MHz LNA.

Receive portion Receive signals from the antenna

relay areamplified by one-half of a modi- fied TV receiveonly low-noiseamplifier (WRO LNA). The other half is used in the transmit portion of the transverter. My first modification involved installing an SMA antenna connector in place of the waveguide antenna inpuL3 Nor- mally a scalar-type feed horn is attached

MHz. As with other bands up to2304 MHz,

the main modesof communications on 3456 MHz are CW and SSB. There are many ways to generate RF power on this band - both CW and linear. Fre- quency multipliers with step recovery diodes (SRDI and active multipliers are used for CW, FM, beacon transmitters, and local oscillators. You can use linear transvertersfor SSBICW and all other modes, just like on the 50 through 2304 MHz bands.

Figure 1 showsthe block diagram of a 144 to 34%-MHz transverter. The transverter transmit and receive mixers use a common local oscillator at 3312 MHz. The 144-MHz transmit i-f is mixed with the local oscillator to produce3456- MHz transmit signals. During reception, the3456-MHz receivesignalsare mixed with the local oscillator to produce the 144-MHz receive i-f signals. A 2 or3 sec- tion interdigital filter follows the trans- mit mixerto attenuate out the local oscil- lator and image freq~encies.',~

68 January 1989

I amplif ier

sn* hrt 1.181

F i l t e r l P w e r Divider

l e p ( X 8 sRD H a l t i ~ H e r u

RX nlxer 3-slege receive amp

Block diagram of a 144-MHz to 3458-MHz linear transverter.

cap is also installed to bring + 15 Vdc into the LNA housing without using an external bias-T attached to the output "N" connector.

Split N R O LNA The greater than %-dB gain LNA is

modified again to make two separate three-stage amplifiers. The amplifier I use is the Amplica model ACD 305331 (90 degree) LNA. The 305331 LNA has two GaAsFET stages followed by four bipolar stages and a filter. Figure 2 shows the "split-in-half" LNA. The

t-- SflA to TX Mixer RF out

10 pf chip cap added

A split TVRO LNA showing two separate 3-stage amplifiers.

than 30-dB gain and a2-dB system noise figure in receive mode.

I modified the LNA by wiring two miniature 50-ohm TeflonB coax cables fitted with SMA male connectors into theamplifier between the third (0.3) and fourth (04) stages. The twocoaxcables should be long enough to go from inside the LNA and connect to the receive and transmit mixersin your transverter. Cut away the microstrip at the interstage DC blocking capacitor to create a gap in the line. Soldera 10-pF chip capto theout- put line of stage 03. This becomes the receive amplifier output. The existing DC blocking chip capacitor becomes the input of the transmit amplifier chain.

Open the other compartment of the LNA. Drill two holes and run the minia- ture coax through the holes into the compartment. Now drill two small holes in the pc board beside each of the two DC blocking capacitorsto pass the coax cable center conductors. Solder the center conductors to the blocking chip caps and solder the shield of each cable to the ground plane at the point where the cable goes through the pc board. The shield relieves strain on the cable, so the chip caps don't break. Apply a dab of RTV or silicone bathtub seal where the cables go through the hous- ing to increase the strain relief and mois- ture proof the LNA.

You now have two separate ampli- fiers. The stability of the receive front end is maintained because the input iso- lator is still intact. It's okay to leave the

FB FB FB

RFC 1 RFC2 RFC3 RFC4

~ 1 2 0 p c 3 c , ~ ~ o p ~ 8 ~ ~ 2 0 p c 9 c 1 3 ~ ) 2 0 P c 1 z

4 7 3 470p 470p 470p

F.T. F.T. F.T. F .T

from A from B from C from D on tL. Bias h a r d i n f lg. 6

RFC 1.2.3.4 3t. '24, 0.1" ID C 1,5,1 1 10 pf chip caps C4,lO Johanson Gigi-trim 4.5 pl JnC '27273 C3,6,9,12 20 pf chip caps FB Ferrite bead

Board Material 0.032' Teflon Double sided Er = 2 55

Q I Thornson/Mostek SD 1850 Q2 Thornson/flostek SD 180 1 z 1 , 9 0.080' (1.2 rnm) X any length 22 0.060- (1.5 mm) X 0.4" ( 10 mm) 23 0.10" (2.5 mm) X 0.30" (7.6 mm) 2 4 0.15' (3.8 mm) X 0 30" (7.6 mm) 25 0.060" ( 1.5 mm) X 0.2' (5 mm) 26 0 060- ( 1.5 mm) X 0 35" (8.9 mm) 27 0 10' (2.5 mm) K 0 25' (6.3 mrn) 28 o 375' (9.5 mm) X 0.275- (7 mm)

--

The 2-stage 3466-MHz linear amplifier.

+ 15 Vdc applied to the LNA; the front so you can use input voltagesfrom 15 to end won't oscillate into the open 28Vdc. antenna relay during transmit. The LNA The receive amplifier output feeds the hasan on-board7812voltageregulator, RF port of the receive mixer. The Mini-

January 1989 m 69

Circuits ZFM-4212 and ZAM-42" are suitable mixers because they are fitted with SMA connectors. The pc board mounted PAM-42 is also a good 3456- MHz mixer. I used the Anzac MD-169 (normally pc board mounted). I enclosed it in a homemade brass hous- ing fitted with SMA connectors.

You can peak the receiveamplifier in a noise figure set-up by tweaking the miniature trimmers mounted through- outthe LNA. Gain can be maximized at 3456 MHz.

Another application for a split LNA in a transverter involves using one half to amplify the very low output of a 3312- MHz schottky diode multiplier for the local oscillator, and the other half to amplifythe transmit mixer SSB output. Try using a second modified 50-dB gain TVRO LNA for the receive amplifier. This approach worked very well for me.

Transmitter stages You can use the same type of mixer

for the transmitter as you did for the receiver. I used the MD-169. Theoutput of the transmit mixer (usually - 10 dBm or so) is amplified by the second half of the split LNA, which provides + 10dBm (10 mW) output. The three bipolar stagesand filter provide an excellent lin- ear amplifier for low-level signals.

Two-stage linear amplifier A two-stage linear amplifier, provid-

ing20-dB gain and + 27dBm (500mW) power output at l-dB compression, fol- lows the modified TVRO amplifier. The amplifier is shown in fig. 3. It was built into one enclosure to eliminate two SMA connectors, and to reduce its overall size. The amplifier is built on 1/32" Teflon double-sided pc board (Er =2.55), using microstrip matching networks (seefigs. 4and 5). Although the two stages are etched on one pc board and housed in the same enclosure, you can build two separate amplifiers. The DC blocking capacitor (C5) is mounted in a 50-ohm line; the two stages could be separated at this point. Use DC blocking capacitors on the input and output of both stages.

'Mini-Circuits, P.O. Box 166, Brooklyn, NewYork 11235. (7181 9344500.

O C H I P CAPS CI . 3. S. 6. 9.11 4 N D 12 HOUSING IS 3 3.IB4mmJ x 15- f3BmrnJ x 0 5.tr3rnmJ BRASS STOCK. MILLED TO ACCEPT P C BOARD

Component placement of the 2-stage 3456-MHz amplifier. All components mount on the trace side of the pc board.

Full scale artwork for 2-stage amplifier on 1132" Teflon" double-sided pc board. Er =2.55. Opposite side (ground plane) is unetched.

Make all DC and RF grounds low inductance paths through to the ground plane side of the Teflon pc board. Do this by putting multiple rivetsthrough to the ground side. Another method is to cut small slits into the board with an Xactom knife, and insert and solder strips of copper foil on both sides.

All theamplifiers I build for 1296 MHz and up are constructed from milled-out &ass housings. I solder the Teflon pc board into the brass enclosure, and mill two slots in the brass housing to accomodate the flanges of the two tran- sistors. The bypass capacitors and tun- ing trimmers are mounted on the pc board close to the board edges. This

allows direct connection to the brass housing and provides good DC and RF grounding. Holesdrilled in the brass box enable you to externally tune the unit with a plastic tuning tool.

The input and output connectors of an amplifier should also be soldered to the ground plane side of the pc board. In my amplifier, I attached the two SMA connectors to the brass box with 2-56 screwsand then soldered them perma- nently. I performed this step on a hot plate when I soldered the pc board in place. You could also solder the con- nectors on the ends of the pc board in a "launcher" configuration with the cen- ter pins of the connectors mounted and soldered parallel to the microstrip.

70 January 1989

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to connecttons in Fig. 3

IOUfd FB D l FB

+ 28 Vdc IN

1 W 20V R2 R I

Resistors are 1/4 watt except where noted LM317T

C 16.20.21 10 ufd/35 Vdc electrolytic I -adjust C23.24 1 ufd/35 Vdc Tantalum D I 1N5248B 18 V/500mw zener diode R1 2 0 0 1/2 watt R2.3 2 0 1/2 watt 1 ::!: R5 10 KO mlneture pc mount pot R7 100 0 minature pc mount pot U1 LM317T Posltlve regulator I -adjust

U2 Lfl337T Negatlve regulator ' ?-"In

FB Fernte beads 3-vout

Bias sources for the 2-stage 3466.MHz linear amplifier. Both regulators are mounted on a heatsink with mica insulators, shoulder washers, and heatsink compound.

Amplifier biasing The first amplifier stage (Q1) is a com-

mon emitter Thomson SD 1850 transis- tor,' operated as a Class A amplifier. The SD 1850 can be used asa 150-mW Class A linear amplifier from 432 to 3456 MHz. Q1 uses standard zener diode biasing. The sec'ond stage (02) is a Thomson SD 1801 transistor (a 1 to 2 watt11 to 3 GHz CW transistor). 02 is a common base transistor (operating Class AB), and requiresa negativevolt- age for bias in addition to the28-Vdc col- lector supply.

I have fotward biased many common base devices in the past - many are being used on 1296 and 2304 MHz. In most cases linearity is as good as with a common emitter amplifier. Because microwave power output is at a premium, Amateurs running common base linear amplifiers usually run them closer to power saturation (P,,), rather than in the linear region. This is why the amplifier may sound slightly rough.

Other than a few local SSB ragchews, most communicationson 2304and 3456 MHz are on CW.

Low-power devices like the 1-watt SD 1801 areeasyto bias linearly. Higher power devices like an SD 1597 transistor" require a little more care and a higher current biassource. A com- mon base linear amplifier requires mainly that the bias source be of very low impedance. This is true for the - 5 Vdc supply, as well as the associated components of the LM337T regulator. Use an LM337K for higher power com- mon base amplifiers. The regulator in a TO-3 style case is capable of higher power dissipation.

The two bias sources in fig. 6 were made on an etched G-10 double-sided pc board (shown in thefigs. 7and81. All 'SGS-Thomson Microelectronics, Commerce Drive, Montgomeryville, Pennsylvania 18936,12151 362-8500. All Thomson transistors are available through: RF Gain. Ltd., 100 Merrick Road, Rockville Centre, New York 11570. 1516) 536-8868 and 18001 646-2322. "TheSD1597 isaThomson25wan/l296MHztransis- tor for Amateur applicat~ons.

'5 I

THE ARRL

REPEATER DIRECTORY

CONNECT! Interested in packet radio? The 1988-1989 ARRL Repeater Direc- tory is for you. This is the most complete compilation of digi- peaters ever. There are over 1400 listed! The regular repeater user will find over 13,000 listings plus band plans, addresses of fre- quency coordinators and CTCSS (PL) tone chart. Pocket size. Avail- able at your dealer or directly from ARRL for $5.00 plus $2.50 for shipping and handling ($3.50 for UPS.) r / 151

r / 152 January 1989 75

0

0

Full-scale artwork of bias board. Etched side shown. Oppositesideisthe ground planeand is unetched. Board material is 1/16"(1.6 mm) G-10 double sided.

C BOAR0 -- SOLDER TO EACH FEEDTHRU CAPACITOR NUT PIECES OF TINNED WIRE ARE CONNECTED FROM POINTS A, 8 , C AND D TO FEEDTHRU CAPACITORS

non-ground holes must be "cleared" on the unetched side to prevent compo- nent shorting. Begin by drilling the non- Component placement on the bias board, showing x-ray view of the traces. Parts

ground holes. Remove the copper by are mounted ontheground planesideof thepc board, which isunetched. Clear

counterboring the holes with an over- all nonground holes on this side of the board. Solder all grounds on both sides of the board of points "x".

sized bit. Set the depth of the hole to about half the pc board thickness. Drill diode conducts and biases on 01. Set dimensions would stay the same and theground holes last to prevent confu- the optimum current while tuning the thestage would be tuned up in thesame sionaboutwhich holesgetcleared. Sol- amplifier for power output. manner as a linear one. der components or wiring connected to I used an LM337T (U2) as the nega- ground on both sides of the board, as tive bias source for the output stage Tune-up indicated by an "x" in fig. 8. (02). The output voltage of U2 is halved While I was tuning my amplifier, the

Solder the ground plane side of the pc by voltage divider R2-R3, because 1.2 two piston trimmer capacitors peaked at board directly to the ground posts of Vdc is about as low as a three-terminal minimum capacitance. To bring the feedthrough capacitors C2, C7, C8, and regulatorwill go. Note that the - 5Vdc trimmers into range, I had to trim off C13 as shown in fig. 8. Do this so that supply must haveafloating negativeter- some of the microstrip capacitors with the bypass capacitors C14, C15, C16, minal. Peak the idling currentwhiletun- an Xacto knife. I'd used the microstrip C17, C18, and C20 will be close to the ing for power output. The - 5 Vdc is dimensions for some single amplifiers amplifier (where they will bypass RF applied to the amplifier bias board dur- that I designed and built earlier. Not most effectively). Use small-gauge ing transmit only. This minimizes heat- going out to 50-ohm connectors inter- tinned wire to connect the bias board to ing and possible oscillations into the stage produced slightly different imped- the feedthrough capacitors. open antenna relay during receive. ance matching. Other than this, the

Two power-supply voltages ( + 28 If maximum ratherthan linear power amplifier came right up to power and Vdc and - 5 Vdc) are supplied to the output (for a rover rig, for example) is a gain expectations. Theartwork in fig. 5 board. You can also build a powersup- requirement, you could operate thesec- reflects the microstrip dimension ply that providesall the positivevoltages ond stage Class C with greater than 1 - changes. for a complete transverter (including watt power output. This would elimi- To tune this amplifier and most of this bias b ~ a r d ) . ~ A n LM317T (U1 )sup- nate the negative power supply (possi- others I've built, I used the following plies a variable collector voltage for Q1. bly a 6-volt Gel cell or lantern battery). equipment: a Wavetek 2005 RF gener- Adjust the collector voltage without You'd ground theemitter of Q2 by con- ator, HP435B power meters, and an HP power input (Pi,), until the 18-Vdc zener necting RFC2 to ground. The microstrip spectrum analyzer (part of an RF test

76 January 1989

station at Thomson). You'll need an RF interested in is the short-term stability. generator and a "real" power meter to The actual freuuencv operated on at check linearity. DO this by changing the Pi, in I-dB steps, while looking for the same change in the output. Use the spectrum analyzer to check gain and linearity. Also look for spurious responses.

Now, set thequiescent current (idling current without power input). Attach a 50-ohm load to both the input and out- put connectors. Adjust both bias adjust pots (R5 and R7) for minimum voltage as measured on the output of U1 and U2. Do this before making connections to the amplifier, to prevent transistor damage. Adjust the 01 collector current to 80mA with a current meter con- nected in series with the 20-ohm resis- tor (R1 1. Next, adjust the collector cur- rent of Q2 to 50 mA with a current meter in series with the collector supply feed- through capacitor (C13).

Apply 5 mW of 3456-MHz RF to the amplifier input, with a power meter and spectrum analyzer anached to the out- put. Adjust the two trimmers (while looking at the analyzer and power meter) for maximum output.

The two-stage amplifier will produce maximum power output with 10 to 12 mW of drive. You can readjust the idling current on each stage slightly, under power output conditionsfor either max- imum gain or maximum power output. It's possible to adjust the idling current of 01 for 80 to 110 mA, and for Q2 up to 65 mA, for proper operation. The total current at 28 Vdc will be 200 to 250 mA when the two-stage amplifier is running at maximum power output.

My two-stage amplifier performed as follows: Power output at 1 dBc +27.6dBm (580 mW)/Gain = 19.8 dB PSat +29.3 dBm (850 mW)/Gain =

18.9 dB

Local oscillator The local oscillator is probably the

most important part of a transverter. It sets the transverter's frequency stabil- ity. The i-f frequency is usually verysta- ble and accurate, because it's almost always a commercially made trans- ceiver. Of course, all we're really

3456 MHz can vary many k ~ z over nor- mal temperature ranges. If you need the exact frequency (i.e., for schedules), use a frequency counter. If a 3.5-GHz counter is unavailable, measure a lower frequency stage of the local oscillator chain on a UHFcounter. The3312-MHz local oscillator frequency will give the 3456-MHz transmitlreceive frequency.

The local oscillator chain in my trans- verterstartsout with a surplus400-MHz telemetry transmitter strip, which uses a temperature-compensated crystal oscillator. You can find surplus crystal- controlled strips at flea markets; they make stable microwave local oscillator sources.

Step recovery diode multiplier

The 400-MHz module (crystalled up for 414 MHz) drives a X8 step recovery diode (SRD) multiplier (fig. 9). The mul- tiplier functions as follows: A pi- network input circuit is used between the 414-MHz module and the SRD, to provide some impedance matching into thediodeat414 MHz. The output of the pi-network (C3) connects directly to the input of the SRD holder. The SRD pro- vides a comb output, consisting of many harmonics of the414-MHz driving signal. The RF is coupled into the4-pole comb filter, which filters out the wanted signal (3312 MHz). Dual SMA connec- tors on the filter output provide the local oscillator signal to both mixers in the transverter.

Most SRDs are packaged without wire leads and require special clamp- type holders for mounting and heat sinking. You can makea brass housing to hold the SRD and provide output coupling into the4-polecomb filterthat follows. Figure 10 shows the SRD holder. Clamp the step recovery diode between part no. 4 (the RFinput/output connection) and part no. 6 (a 1/4-20 brassset screw). Use a dab of heat sink compound where the SRD mounts into part no. 6; this aids thermal conduction to the main housing. I made the brass diode holder on a milling machine to fit into the input end of thecomb filter. You

L I 0 2- (5 mm) X I 25' (32 mm) brass strlp C 1.2.3 lOpf Johanson trlmmer JHC -5200 C4 001 Ufd dISC R I z I KO (adjusl lor performance) DI HP 5082-0320 step recovey dlode or HP 5082-0800 or MIA-Comm MA 44608- 1 or TRW A45365 Or Thomson OH252 or DH256 RFCl 121. '24. 1/8' (3mm) ID

X8 SRD frequency multiplier and filter.

can make a functional unit with ordinary hand tools.

Depending on the SRD, you can make the 1/4-20 brass set screw (part no. 6 ) with the appropriate mounting hole. Some SRDs have 3-48 UNC threaded posts that would screw into part no. 6. You could use a glass- packaged SRD by making a Teflon spacer with the glass diode mounted in the center. Fold the wire leads over at both ends and clamp the Teflon spacer into the diode holder.

Attach the SRD holder to the comb filter asin fig. 11. It'spossible to usean interdigital filter, but a comb filter is eas- ier to mount and tune up because the tuners are on one side.'s2 A comb filter uses the same dimensions as an inter- digital type, but is configured with all the tuning elementson thesameside. I used all brass construction. The end wallsare 1/4"thick brassstock. Drill holesforthe four filter poles, and on the opposite side for the four tuning screws. Solder two SMA connectors to the sheet brass covers. Anach the two covers with 2-56 x 3/16" screws to hold the filter together while soldering all joints on a hot plate.

After you've built the filter, attach the SRD holder to it with 2-56 x 3/16" screws. Usea small piece of sheet brass as a mounting platform for the pi- network input circuitry. Attach this assembly to the filter so the SRD input connection (part no. 3) is in close prox- imity to the trimmer capacitor (C3) of the input circuitry.

January 1989 77

Apply the 414-MHz RF to the SRDIfilter assembly. Adjust the input network and the filter for maximum power output with a power meter attached on one output port, and a 50- ohm load and spectrum analyzer on the other. Use a spectrum analyzer during tune-up to ensure a clean local oscilla- tor output. Adjust the output coupling probe by threading it in or out of part no. 4. First loosen part no. 3, then tighten it up after the output coupling is optimized. You'll need to adjust the414- MHz drive for proper output at 3312 MHz (5 to 10 mW at each output con- nector). The two outputs will be within 1 dB of each other - more than suffi- cient to properly supply a local oscilla- tor signal to the two transverter mixers. You can change the 414-MHz drive using an LM317T voltage regulator which supplies an adjustable collector

voltage to the414-MHz output stages. In my transverter, power input at 414 MHz was 500 to 600 mW. I made no attempt at optimum input/output matching of the SRD; power at UHF is easy to come

I provided two outputs on the comb filter instead of using a 3-GHz power divider to split the local oscillator for the two mixers (see fig. 11). This is a very simple power divider and you can use it on any comb or interdigital-type filter. You can take two different levels off the filter (for use in a duplex system) if one output uses capacitive coupling. For example, the center pin of an SMA con- nector provides coupling = 15 dB down from a normally connected output.

There area number of combinations for the local oscillator chain. In addition to what's shown in the block diagram, you could also generate 3312 MHz using

Mate r~a l i s brass stock. 0.82- (2 1 mrn) X 0.82" (2 I rnm)

x 0.82" (21 rnm)

O u t ~ u t End view 0 u t G t coupling probe. 2-56 X 0.75' ( 1 grnrn) brass screw w i t h a 0.2' (5rnrn) brass disc soldered on the end

&ill -24 for d r 5 0 m t k d

SRD holder end Flller

Inside diem. i s -2 I - part * 4

Tel lon bushing 0.20 1- (5.1 mm) dlarn. and 0.45- ( 1 1.4 rnm) long, d r i l l end fo r 2-56 screw (-3)

drill end tap 2 PI- for

* 4 '3 i s a 2-56 X 1 .O" (25rnm) brass scl

and connects t o C 3 i n Fig. 9

dlarneter brass piece F i l t e r

(top view) *5 i s the SRD mounted betweenS4 and the 1/4-20 brass set screw.

*6 i s a 1/4-20 NC brass set screw w i t h a screwdriver s lo t cut i n one end and s hole drt l led i n the other fo r the SRD.

*7 i s a te f lon bushing 0.201" (5.lrnrn) diameter. This bushing supports the

Dual local osci l lator outputs output coupling probe and i s dr i l led f o r the 2-56 screw

3456-MHz SRD holder and output coupling detail.

0 25' 16 -1 x o n - 1 9 m n ) -

X 3 40Y81 mm) b... 't*

SNA

output - 1

The SRD/Filter/Power divider assembly. At top, the SRD holder is shown mounted to the +pole filter. The middle is a cut-away view showing the position of the SRD out- put probe and dual local-oscillator outputs. The bottom is the end view filterlpower divider. Connector input-output taps are 0.25" (6 mm) from the cold end.

a 1 -GHz local oscillator strip (crystalled for 1104 MHz) driving an active tripler to 3312 MHz. There are a few sourcesfor stable crystal-controlled 1 -GHz local oscillator chains.*

Active frequency multiplier FigurelPshowsthe x 3to3312 MHz

multiplier. The active device is an SD 1801 transistor ((21). The multiplier is built on 1132"Teflon double-sided pc board (Er = 2.55) and mounted in a brass carrier (shown in fig. 13). The multiplier is connected to a five-section interdigi- tal filter.'r2 I used an SMA connector on theinput instead of the SRD holder. The input connector is tapped at 0.25"from the cold end of the input pole.

The multiplier and filter are connected in the transverter with a small piece of UT-141 semi-rigid coax. The exact length of the cable seems to have an effect on the performance of the mul- tiplier. Try different lengths of intercon-

'Down East Microwave, Box2310, RR I t , Troy, Maine 04987, 1207)948-3741. (W3HOf sells the LMW Elec- tronics, model ULO, Universal Local Oecillator kit.) SSB Electronics, 152-MHz Local oscillator chain for their 2304 MHz transverter, crystalled and retuned to 1104 MHz.

78 January 1989

necting cable to provide the best match intothe filter. The multiplier and filter are effectively one stage and are tuned as such. Again, a power meter is attached to one output, and a 50-ohm load and spectrum analyzer to the other. After tuning the filter for maximum power output at3312 MHz, you can adjust the

1104-MHz drive level to provide the proper level outputsforthe two mixers.

Here's how the multiplier operates. Theinput of Q1 istuned to 1104 MHz (or 1152 MHz in a3456-MHz beacon trans- mitter). The output is tuned to 3312 MHz (or 3456 MHz). An interdigital fil- ter removes the fundamental and sec-

Dual outputs lnput

UT- 141 Semi-rigid coax

Board material i s 0.032' Teflon double-sided Er = 2.55

C 1 3.5 pf Johanson piston (1 I Thomson/Plostek SD 180 l trlmmer, JMC -580 1 or 5802 C2 4.5 pf Johanson Gigi-trim 2 1.7 0.08W (2 mm) X any length 500 line cap, JMC *27273 22 0.150- (3 8 mm) x 0.30' (7.6 mm) RFC 1 61, *26,0.1- (2.5 mm) ID 23 0.060' (1.5 mm) X 0 35- (9 mm) RFC2 31, -24, 0.1' (2.5 mm) ID 24 0.150- (3.8 mm) X 0.30- (7.6 mm) FB Ferrite bead 25 0.200- (5.0 mm) x 0.30- (7 6 mm)

26 0.060- ( I .5 mm) X 0.20- (5.0 mm)

X3 Multiplier to 3312 or 3456 MHz with a Ssection interdigital filter on the output.

SMA lnput

I I

firass houslng wlth tloard soldered in place

Parts placement on the X3 multiplier and full-scale artwork below. Trace side shown. Op- posite side is unetched.

ond harmonic frequencies and also pro- vides two outputs for the two transverter mixers. The typical perfor- mance of the tripler and filter with one output is 30-mW power input at 1104 MHz (or 11521, which produces40to60 mW output. Pi, of 50 mW produces greater than 100 mW. When running the multiplier on 15Vdc, I'veseen + 23 dBm (200mW)outofoneoftheseunits. You could use this for a beacon trans- mitter. The3312-MHz (3456MHz) out- puts are very clean; all unwanted har- monicsare down greater than 45dB and all non-harmonically related signals are down greater than 60 dB.

I-F and DC switching It's necessary to have some means of

switching the i-f transmit and receive lines when connecting the 2-meter transceiver to the 3456-MHz trans- verter. You'll also need a keying circuit to control the transmitlreceive of the transverter. This requires one of two different hookups - depending on whether the 2-meter i-f will be a trans- ceiver or another transverter (an MMT- 144128, for example*).

Two-meter transverter as an i-f

Separate receive and transmit con- nectors are available on the MMT-144 transverter. The i-f output of the receive mixer is connected to the 144-MHz receive port on the 2-meter transverter. On the transmitter side, you must insert an attenuator between the transmit out- put (nominally 10watts) of the2-meter i-f and the3456-MHz transmit mixer (see fig. 14). Adjust the i-f drive level to the

'Microwave Modules Ltd., Liverpool, England, makes a complete line of VHF /UHF transvertem.

January 1989 79

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Note 7

Note 8 RF C o n t r o l

a l l resistors are 1 / 2 watt carbon

R5 = 50 O minature pc board type p o t

I-f attenuator and adjustable RF control.

transmit mixer as follows: Turn the RF control (R5) CCW (maximum attenua- tion). Attach a power meter to the out- put of the 3456 transverter. Put the 3456-MHz transverter into the transmit mode and apply the 10 watts of drive. Adjust the RF control (R5) for a maxi- mum power output at 3456 MHz. Reduce the2-meter RF; it should show a decrease in the 3456-MHz output. If there's no reduction in power output, the mixer is being overdriven and you must insert additional attenuation in front of the RF control.

It's important that the i-f radio be operated at its normal output level, and not with the gain or CW control turned down. The RF control in thetransverter is adjusted to match the i-f level, not vice versa. Thisensures that the trans- verter will neyer be overdriven, even when the i-f radio's gain controls are adjusted improperly. The procedure is correct for any transverter system.

Two-meter transceiver for the i-f

Figure 15 shows a Pin diode RF switch that provides switching for the2- meter i-f during transmit and receive. The i-f transceiver is connected to the Pin diode switch; this gives two sepa- rate ports similar to the outputs of the2- meter transverter described earlier. The R F attenuators* and R F control arealso used in this installation. The i-f drive adjustment is the same as if you were using a transverter. Don't make changes in the RF drive with the2-meter transceiver in the "low power" position or you'll be asking for trouble.

2-meteF3q ~ ~ ~ ~ ~ ~ o r ! ~ l ~ O f 19 I 3 xcvr

in'Du' 001 u fd L I C4 001 urd pH from receive rnwer I.

D2 - .f port

D 1 .D2 BA 182, nP3340!, or UM9401 Pln dlodes (P~III~S, notorols. Unltmde respecllvely) RFCI 101. -24. 118-(3 mm) ID L I 1/4 Wavelength equlv = 121. -24, 3/32'

( 2 mm) ID c I-co 001 urd ~ I S C CODS

I I

Pin diode RF switch.

DC control circuits Control the 3456-MHz transverter

with "hard keying." Use RF sensing onlyasa last resort. Hard keying is sim- ple. Take a transmit voltage off the i-f radio - either via an accessory jack, or by going inside and soldering a wire to a resistor lead. You just need a voltage between 5 and 18 volts on transmit at a few milliamps of current. Check your radio'sschematic to determine where to look with a voltmeter. Figure I 6 shows a DC switching circuit that provides 12 voltson transmit to control the Pin diode switch in fig. 15. The 12 volts will also key your 3456-MHz transverter control circuits and power supply4.

'Microwave Modules R F Anenua to r Models: M M R

3/25=3dB/25 wan, M M R 713= 7 d B / 3 wan , M M R

15 /10= 1 5 d ~ / l o w a n

/ 155

80 [irP January 1989

v Ground on "i , 1 I Input transmi t

1 N400 1 1 KO

+5- 18 VdC TIP32 onTXfrom 2N2222A 1-f radio HPS-A 13

3 KO

+ 12 ~ d c output on transmit

All resistors are 1/2 watt

C E B C

TIP30 2N2222A HPS-A 13 TIP32

-

DC switching circuit, controlled by the i-f transceiver in the transmit mode.

Antenna relays You can use antenna change-over

relays manufactured by Transco Prod- ucts, Inc. (and other manufacturers) at 3456 MHz. Lookforsurplus relaysatflea markets. Some have specially made connectors designed for the military. Unfortunately, matching connectors usually aren't available. I use a Transco latching-type relay, PIN 82132-909C. It cost me $5.00ataflea market. The con- nectors resembled an SMA female jack, but had male center pins. I removed the threaded-in connectors and installed female SMA connectors. Insertion loss, measured at3456 MHz, isO.1 dB; isola- tion is greater than 60 dB. Surplus relays manufactured by Electronic Specialty Company are usually good for3456and 5760 MHz.

Conclusion The design for this transverter is rela-

tively simple. A few basic components areall you need to build a "bare-bones" unit for mountaintop work. Besides the local oscillator, two mixers and the "split" TVRO LNA will get you on the air. You can use manual transmit- receive change-over (moving a coax cable between RF ports) with good results, asspeed isn't usually a require-

ment. Microwatt transmitters and diode receivers are adequate for most line-of- sight communications. You can always add fancy switching and higher power output later.

You can usesomeof the component designs for other microwave projects. For example, the SRD multiplier issuita- ble for a beacon transmitter. The HP 5082-0320 diode is capable of much more power output at 3456 MHz than is used in this transverter. It's possible to find other 1 to 5-watt SRDs that will fit into the same holder. Try using the active multiplier forthe output or driver of a beacon transmitter. Adjusting the collector voltage and RF power input for maximum yields200 to300-mW power output.

This transverter is one of many pos- sible designs." Microwave enthusiasts in other parts of the country are using surplus phase-locked sources for their local oscillators. TVRO mixers are also in service. GaAsFETS and surplus tube- type amplifiers are being used for the transmitters. There's also an assort- ment of TVRO, surplus, and homebrew GaAsFET receivers at work.

The majority of activity on this band comes from mountain-topping stations and local QSOs. Many stations will soon be on the 3.4-GHz band, and QSOs

similar to 2304 MHz will be common- place. Besides the parabolic antennas normally used on the microwave bands, the loop Yagi is becoming a popular antenna for 3456 MHz.""

"The ARRL Handbook ""Down East Microwave, Box 2310, RR #I, Troy, Maine 04987, (207) 948-3741 sells loop Yagi antennas for all bands 902-3456 MHz.

References 1. Bob Atkins, KAlGT. "TheNew Frontier." QST, May 1984, page 77. 2. R. Fisher, W2CQH, "Interdigital Filters," QST, Janu- ary 1974. 3. Bob Atkins, KAlGT, "The New Frontier," QST. August 1987, page 59. 4. DaveMascaro, WA3JUF. "TransvenerSwitching Dis- play and Universal Transverter Power Supply," QEX, August 1987. page 8. 5. Hewlett-Packard Application Notes no. 913and920, May 1967. 6. R.E. Winkelmanand E.G. Cristal, MicrowavesandRF, September 1970, page 34.

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